The objective of this study is to examine the hypothesis that adaptive changes in response to intestinal resection and bypass take place in the smooth muscle of the small intestine. The hypotesis will be tested by investigating physiological, anatomical, and biochemical parameters in intestinal smooth muscle after the operations. Resection and small bowel bypass will be performed in rats. Smooth muscle and mucosal enzyme activities will be evaluated at various times after surgery in both the bypass segments as well as the functioning intestinal remnant. Physiological changes in muscle activity will be determined by monitoring the transit of a nonabsorbable marker through the intestinal lumen and by monitoring the contractile activities of isolated strips of smooth muscle. Anatomical changes will be determined by measuring the size and weight of the mucosa and muscle layers and by measuring the size of individual muscle cells. Biochemical changes will be determined by monitoring the DNA and protein contents, the levels of glycogen and ATP, and the respiratory capacities of the muscle cells; and by measuring activities of mucosal disaccharidases.